There is known a common rail fuel injection device arranged to supply a high pressure fuel into a common rail by using a high pressure fuel pump which is mechanically driven by an output of an internal combustion engine, and to open fuel injection valves of cylinders connected to this common rail to inject the fuel, by a driving pulse signal.
For example, a plunger pump which is driven by a cam provided to a cam shaft of an intake valve side or an exhaust valve side is often used as the high pressure fuel pump, like a patent document 1. In a middle of a discharge process in which the plunger is pressed by the cam, a spill valve releases a pump chamber. With this, a substantial discharge amount of the plunger pump, that is, a fuel pressure within the common rail is adjusted.
In a case of a structure in which the cam shaft is driven through a chain by a crank shaft, the high pressure fuel pump is mechanically driven through the chain by the crank shaft.
In the structure in which the high pressure fuel pump is mechanically driven in this way through the chain by the crank shaft, a reaction force according to the pump drive is acted to the chain. Accordingly, when the fuel pressure within the common rail is extraordinarily increased by some abnormal state such as the malfunction of the spill valve, the variation of the tension of the chain and the peak value of the tension becomes excessive. This is not preferable for the durability of the chain, and so on.
Besides, a patent document 2 discloses that the fuel injection is immediately stopped for protecting the engine when the abnormal state of the fuel injection device is sensed. However, it is not preferable that the drive of the internal combustion engine is immediately stopped in a case where the vehicle needs to continue to run.